1. Field of the Invention
The present invention relates to a servo control system for controlling a servo motor of a machine tool grinding an inclined surface.
2. Description of the Related Art
Generally, in a surface grinder, a horizontally disposed workpiece is swung with respect to a fixed grindstone, and thereby a plane surface of the workpiece is ground. Alternatively, the workpiece may be ground by swinging the grindstone with respect to the fixed workpiece. A numerical controller connected to the surface grinder controls a motor for a swing shaft for swinging the workpiece or the grindstone and a motor for a feed shaft for feeding the workpiece or the grindstone in a direction perpendicular to the swing shaft.
FIG. 9 is a schematic diagram illustrating a workpiece and a grindstone according to the conventional technique disclosed in Japanese Laid-open Patent Publication No. 2011-194552. As illustrated in FIG. 9, when an inclined surface of a workpiece W is ground, the workpiece W is inclined around a tilt shaft. Accordingly, as in the case of grinding the plane surface, the inclined surface of the workpiece W can be ground by a grindstone G.
FIG. 10A is a graph illustrating a relationship between a feed position of a feed shaft and a position of the swing shaft according to the conventional technique. As illustrated in FIG. 10A, motion of the swing shaft in the surface grinding is represented by a saw-tooth shape where the swing shaft moves back and forth from one end of the workpiece to the other end. A moving speed of the grindstone from a point P to a point Q in FIG. 10A is approximately constant as illustrated in FIG. 10B. This case is advantageous in that a grinding amount during the grinding is constant.
However, in the configuration illustrated in FIG. 9, a tilt shaft is necessary in addition to the swing shaft and the feed shaft. As a result, the grinder including the swing shaft, the feed shaft, and the tilt shaft has a problem that a configuration thereof is specialized only for grinding a plane surface such as an inclined surface.
As can be understood from FIG. 10A, due to larger torque at the time of acceleration/deceleration, there is a limit to move the grindstone along the swing shaft at a high speed. Moreover, the moving speed suddenly changes, especially at the point P and the point Q. Thus, when the grindstone is moved along the swing shaft at a high speed, a problem of undershoot or overshoot may occur at turns such as the point P and the point Q. This problem may also occur when grinding a conical surface of a conical or truncated cone workpiece (not illustrated) by a cylindrical grinder.
The present invention has been made in view of such circumstances, and has an object to provide a servo control system capable of grinding an inclined surface without needing a tilt shaft and without generating any undershoot or overshoot at turns.